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We may not have this yet.
But I need clarification: does the event have to be world-changing or negative? I believe it can count any event so long as it could potentially personally affect the dead guy. I don't event think the guy has to be dead, depending on the context; he may simply left the place before some event happens on that place.
Related is Slept Through the Apocalypse: he's not dead, but he wouldn't experience the apocalypse; he would only feel the aftermath.
We can never truly eradicate the coronavirus, but we can suppress its threat like influenza^^ First off, that was really rude.
Second, how is a character dying before a major event important plot-wise? Because unless the death affects the plot, then it's just PSoC.
For example, is this character a Magnetic Hero who would have united the survivors of the nuclear holocaust and their death left everyone stranded? Were they a Barrier Maiden whose death enabled the disaster to happen in the first place? Did they die before their child was born?
- Fly, robin, fly! - ...I'm trying!^ True. However, that still doesn't explain the OP's question about "someone gets killed the day before a nuclear war and is spared the horrible fate of living in that new world, etc.". Who is that someone? Are they plot-important or are they just a "lucky" sob?
I feel that more context is necessary in order to determine which trope is applicable in this case because from the way the question is phrased, I'm guessing that the OP is asking about a random Joe who died before the apocalypse.
Edited by RoundRobin - Fly, robin, fly! - ...I'm trying!

I'm just wondering if there's a trope for characters who die very early and never get to experience a world-changing event or the world after it.
Example: someone gets killed the day before a nuclear war and is spared the horrible fate of living in that new world, etc.